1. Field of the Invention
The present invention relates to an image: forming device.
2. Related Art
Normally, image forming devices, such as laser printers, are provided with thermal fixing devices for performing fixing operations. The thermal fixing device includes a heat roller equipped with an internal heater, and a pressure roller that applies pressure to the heat roller. Toner image transferred onto a recording sheet is fixed by heat as the paper passes between the heat roller and the pressure roller.
In some of this type of thermal fixing device, a cleaner is disposed in contact with the surface of the heat roller for cleaning toner adhering to the surface of the heat roller during the fixing operation.
Japanese unexamined patent application publication No. HEI-2-176689 describes one example of a cleaning method. In this method, the heat roller is rotated a prescribed number of times while the periphery of the heat roller contacts the cleaner a plurality of times in order to remove the large amount of resin and coloring agent adhering to the periphery of the heat roller. This cleaning operation is performed after an operation-halt period is over, for example, when paper jam is cleared.
However, the toner removed from the surface of the heat roller adheres to and solidifies on the cleaner. Therefore, if the heat roller starts rotating before the solidified toner on the cleaner is sufficiently melted, the toner can generate abnormal noises from scraping and can damage the heat roller and the like. Hence, during a warm-up operation executed to prepare for a printing operation, the internal heater of the heat roller is first turned ON, and the process waits until the surface of the heat roller reaches a predetermined temperature so that the toner fixed to the cleaner is sufficiently melted by the time of when the heat roller is driven to rotate.
Once the heat roller reaches the predetermined temperature, the toner on the cleaner is sufficiently melted by heat. Hence, when the warm-up operation is executed directly thereafter, the toner adhering to the cleaner has already been melted, even if the temperature of the heat roller has dropped below the predetermined temperature. Therefore, if the process in the image forming device always waits until the heat roller reaches the predetermined temperature before start driving the heat roller to rotate, this waiting time becomes wasteful and prevents the image forming device from achieving high-speed printing processes.